Magnetic properties may be conferred to a wide range of liquids such as hydrocarbons, water, glycerol, silicones and fluorocarbons. These colloidal despersions form a unique class of liquids (called ferrofluids) in which it is possible to induce substantial magnetic forces that result in liquid motion. Conversely, the liquid property of the ferrofluid can be utilized to effect an impedance change in a magnetic bridge or other balanced transformer.
The structure of ferrofluids and the process by which they are produced is adequately described in the literature*. In brief summary, a ferrofluid consists of a dispersion of single domain ferromagnetic particles (e.g., powdered iron-oxide). In order to effect coupling of such particles to the bulk liquid phase, it is necessary to add an ionic or molecular compound whose structure is such that it can both adsorb on the surface of the particle and be solvated by the carrier liquid. This results in the formation of an essentially bound liquid sheath around each particle. A typical compound is oleic acid (a well-known stabilizing agent for dispersions in aliphatic hydrocarbons) which contains a polar carboxylic moiety that is similar to the dispersing medium in chemical composition. FNT *"Some Applications of Ferrofluid Magnetic Colloids" by Robert Kaiser & Gabor Miskolczy, IEEE Transactions On Magnetics, September 1970.
Since ferrofluids have a high magnetic permeability, they can be used to provide a variable inductance and/or variable coupling transformers, and although the use of conventional fluids in level and attitude sensing devices is well known, there has been no attempt to utilize ferrofluids in a level sensing device to provide a direct electrical readout. What is actually desired therefore, is a simple, inexpensive level sensing device which will generate an electrical signal which is dependent upon the attitude of the device.
Accordingly, a primary object of the present invention is to provide a two axis attitude sensor.
Another object of the present invention is to provide a means for utilizing the high magnetic permeability of a ferrofluid as a level sensing medium.
Other objects and advantages of the present invention will be obvious from the detailed description of a preferred embodiment given herein below.